Recently, the needs for detecting a weak magnetic field increasingly grow such as the need for detecting a magnetic field in an organism, the need for detecting a defect, and the need for the detection without damages.
In the detection of a weak magnetic field, it is important to effectively intake the magnetic field of the detection subject in the magnetosensitive direction of the magnetoresistive effect element. In addition, the change rate of resistance in the magnetoresistive effect element varies due to the variation of ambient temperature and the input of the magnetic field detecting sensor changes accordingly, which is a problem called temperature drift. Additionally, there are also some general problems concerning the reduction of manufacture cost and the miniaturization of the sensor.
According to Patent Document 1 (JP-A-2009-276159), a bridge circuit which is connected to a plurality of magnetoresistive effect elements whose output resistance value changes in response to the direction of the input magnetic field and is capable of detecting the differential voltage between specified connection points is provided. Furthermore, the magnetoresistive effect elements are disposed to make all the fixed magnetization directions of these magnetoresistive effect elements face the same direction. Also, a magnetic body which changes the direction of the magnetic field input to the magnetoresistive effect element is disposed around the bridge circuit mentioned above.
In particular, the following configuration is used for the magnetic field detecting sensor. The bridge circuit is provided with four mentioned magnetoresistive effect elements, and the element forming part in which two magnetoresistive effect elements which become a pair and are adjacent to each other but are not connected in the bridge circuit are formed at almost the same place is formed at two places corresponding to each pair of the magnetoresistive effect elements, the magnetic body mentioned above is disposed between the element forming part formed at these two places.
With the configuration of the magnetic body mentioned above, the detection magnetic field of one direction can change towards different directions among these magnetoresistive effect elements, the magnetic field enters one magnetoresistive effect element in the fixed magnetization direction, and the magnetic field enters another element in the opposite direction. Thus, an improved detection accuracy of the detection magnetic field in one direction can be expected because a large differential voltage is output from the bridge circuit.
Further, according to Patent Document 2 (JP-A-2010-276422), the bridge circuit is composed of a GMR element, and a magnetic body is disposed in such a manner that the magnetic field in a direction perpendicular to the fixed magnetization direction of the GMR element becomes the detection magnetic field.
Further, a solenoid coil is provided to generate other magnetic field in a direction opposite to that of the detection magnetic field (i.e., in a direction to eliminate the detection magnetic field), a controller is provided to control the current via which other magnetic field is generated in the solenoid coil.
The solenoid coil mentioned above is disposed to surround a sensor with the bridge circuit formed inside, and the bridge circuit is located on the center in the left-to-right direction and also on the center in the height direction.
The controller mentioned above controls the current used for inputting the value of the detection magnetic field (i.e., the value of the differential voltage output from the mentioned bridge circuit) and generating other magnetic field in a direction to eliminate the detection magnetic field in response to the value of the differential voltage.
With the controller mentioned above, the current flowing to the solenoid coil is controlled such that the value of the differential voltage output from the bridge circuit (i.e., the value of the detection magnetic field) becomes zero.
In addition, according to Patent Document 3 (WO2011/081197), the magnetic field detecting sensor has a structure as follows. In particular, the bridge circuit is composed of a GMR element, a pair of permalloy yokes are disposed on both sides of the GMR elements R1 and R3 in the X-axis direction, and another pair of permalloy yokes are disposed on both sides of the GMR elements R2 and R4 in the X-axis direction, a planar spiral coil is disposed on the lower side of the GMR elements as the magnetic field generating conductor for generating other magnetic field in a direction opposite to that of the detection magnetic field.
The bridge circuit composed of the mentioned GMR element, the permalloy yokes and the planar spiral coil are formed in a same stacked body.